Optical projector with beam monitor including mapping apparatus capturing image of pattern projected onto an object

ABSTRACT

Optical apparatus includes a device package, with a radiation source contained in the package and configured to emit a beam of coherent radiation. A diffractive optical element (DOE) is mounted in the package so as to receive and diffract the radiation from the radiation source into a predefined pattern comprising multiple diffraction orders. An optical detector is positioned in the package so as to receive and sense an intensity of a selected diffraction order of the DOE.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication 61/261,336, filed Nov. 15, 2009, and of U.S. ProvisionalPatent Application 61/300,465, filed Feb. 2, 2010, which are bothincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to optical pattern projection,and specifically to monitoring the performance of a projector.

BACKGROUND OF THE INVENTION

Optical pattern projection is used in a variety of applications, such asoptical three-dimensional (3D) mapping, area illumination, and LCDbacklighting. In some applications, diffractive optical elements (DOEs)are used in creating a desired projection pattern. DOE-based projectordesigns are described, for example, in U.S. Patent ApplicationPublication 2009/0185274, whose disclosure is incorporated herein byreference.

SUMMARY

The performance of optical projectors of a given type may vary initiallydue to manufacturing tolerances and subsequently due to conditions inthe field. In some applications, it is important to ensure that suchvariations to not exceed certain limits.

There is therefore provided, in accordance with an embodiment of thepresent invention, optical apparatus, including a device package and aradiation source, which is contained in the package and configured toemit a beam of coherent radiation. A diffractive optical element (DOE)is mounted in the package so as to receive and diffract the radiationfrom the radiation source into a predefined pattern including multiplediffraction orders. An optical detector is positioned in the package soas to receive and sense an intensity of a selected diffraction order ofthe DOE.

In some embodiments, the optical detector is configured to output asignal that is responsive to the intensity, and the apparatus includes acontroller, which is coupled to receive and process the signal so as tomonitor a performance of the apparatus. Typically, the controller isconfigured to inhibit an operation of the apparatus when the signal isoutside a predefined range.

In a disclosed embodiment. the radiation source includes a laser diode.

The selected diffraction order may be a zero order of the DOE, and theoptical detector may be positioned so as to receive the zero order thatis reflected back from the DOE. In one embodiment, the DOE is tiltedrelative to an axis of the beam emitted by the radiation source so as todirect the back-reflected zero order toward the optical detector.

In another embodiment, the selected diffraction order is a high order ofthe DOE. Typically, the apparatus is configured to project the patternover a predefined angular range, and the optical detector is positionedto receive the radiation transmitted through the DOE at an angle that isoutside the angular range.

There is also provided, in accordance with an embodiment of the presentinvention, an optical method, which includes transmitting a beam ofcoherent radiation through a diffractive optical element (DOE), mountedin a package, so as to diffract the radiation into a predefined patternincluding multiple diffraction orders. A performance of the DOE ismonitored by sensing an intensity of a selected diffraction order of theDOE using an optical detector positioned in the package.

There is additionally provided, in accordance with an embodiment of thepresent invention, mapping apparatus, including a projectionsubassembly, including a device package, a radiation source, which iscontained in the package and configured to emit a beam of coherentradiation, and a diffractive optical element (DOE), which is mounted inthe package so as to receive and diffract the radiation from theradiation source into a predefined pattern including multiplediffraction orders. An optical detector is positioned in the package soas to receive a selected diffraction order of the DOE and to output asignal that is response to an intensity of the selected diffractionorder. An imaging subassembly is configured to capture an image of thepattern that is projected onto an object. Processing circuitry isconfigured to process the image in order to produce a three-dimensional(3D) map of the object, and to process the signal in order to monitor aperformance of the DOE.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, pictorial illustration of a system for optical 3Dmapping, in accordance with an embodiment of the present invention;

FIG. 2 is a schematic, sectional view of an optical pattern projector,in accordance with an embodiment of the present invention;

FIGS. 3A and 3B are schematic sectional and top views, respectively, ofa radiation source assembly used in an optical pattern projector, inaccordance with an embodiment of the present invention;

FIG. 4 is a schematic, sectional view of an optical pattern projector,in accordance with another embodiment of the present invention; and

FIG. 5 is a plot that schematically illustrates the performance of aprojector beam monitor, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

Optical projectors based on diffractive optical elements (DOEs)sometimes suffer from the “zero-order problem,” which is described inthe above-mentioned US 2009/0185274: A portion of the input beam of theprojector (the zero diffraction order) may not be diffracted by theprojection optics and may thus continue through to the projectionvolume.

The “efficiency” of a DOE is a measure of the amount of input energythat the DOE diffracts, in relation to the energy of the incoming beam.This efficiency can vary in production due to manufacturing tolerances.It can also change during the lifetime and operation of the projectorfor various reasons, for example:

-   -   Humidity entering the projector can condense on the DOE surface        and lower its efficiency.    -   Vapors of glue (used in the production process) can attach to        the DOE and degrade its performance.    -   Excess heat, due to a malfunction or misuse, can deform the DOE        and lower its efficiency.        Such changes in efficiency, with concomitant increases in the        zero-order intensity, can compromise system performance and may        have various other undesirable consequences.

Embodiments of the present invention that are described hereinbelowaddress this problem by incorporating a built-in beam monitor, in theform of an integral optical detector, into a DOE-based projector. Thedetector signal can be continuously or intermittently monitored by acontroller in order to evaluate the DOE efficiency and inhibit operationof the projector if the signal is outside a certain safe range. Suchembodiments thus prevent eye safety hazards that could otherwise arisedue to DOE efficiency degradation over the lifetime of the projector.

In the disclosed embodiments, optical apparatus comprises a radiationsource, which is contained in a device package and is configured to emita beam of coherent radiation. The radiation source may comprise a laserdiode, for example, and may emit radiation in the visible, infrared orultraviolet range (the spectral regions that are generally referred toas “light”). A DOE, mounted in the package, diffracts the radiation fromthe radiation source into a predefined pattern comprising multiplediffraction orders. An optical detector, such as a photodiode, ispositioned in the package so as to receive and sense the intensity of aselected diffraction order of the DOE. The “selected diffraction order”may be sensed individually, or it may alternatively be sensed togetherwith one or more adjacent diffraction orders.

Various detection configurations may be in different embodiments. Forexample, the detector may sense the zero order of the DOE directly(typically the reflected zero order, in order not to disrupt theprojected pattern). Alternatively, the detector may sense a highdiffraction order transmitted by the DOE, typically at an angle that isoutside the range of the projected pattern itself. A “high order” inthis context means at least the second diffraction order, or possiblythe third, fourth, or still higher order.

Although the embodiments described below relate specifically toapplications involving projection of optical patterns, particularly forthree-dimensional (3D) mapping, the principles of these embodiments maysimilarly be applied in other applications in which there is a need tomonitor the diffraction performance of a DOE.

System Description

FIG. 1 is a schematic, pictorial illustration of a system 10 for optical3D mapping, in accordance with an embodiment of the present invention.Methods and systems for 3D mapping based on projected patterns insystems of this sort are described, for example, in PCT InternationalPublications WO 2007/043036, WO 2007/105205, WO 2008/120217, and WO2010/004542, whose disclosures are incorporated herein by reference.

System 10 comprises an imaging device 12, comprising a projectionsubassembly 14, which generates and projects a pattern onto a region.(In the pictured example, this region contains a human user of thesystem.) Details of possible designs and operation of projectionsubassemblies of this sort are shown in the figures that follow and aredescribed hereinbelow with reference thereto. An image capturesubassembly 16 in device 12 captures an image of the pattern appearingon the user. An image processor 18 processes image data generated bydevice 12 in order to reconstruct a 3D map of the user, as explained inthe above-mentioned PCT publications. Although processor 18 is shown inFIG. 1, for visual clarity, as a separate unit from imaging device 12,some or all of the processing functions of processor 18 may be performedby an embedded controller and/or other suitable dedicated circuitrywithin the housing of imaging device 12 or otherwise associated with theimaging device.

The 3D map that is generated by processor 18 may be used for a widerange of different purposes. For example, the map may be used to providea gesture-based user interface, in which user movements detected bymeans of device 12 control an interactive computer application, such asa game. Alternatively, system 20 may be used to create 3D maps forsubstantially any application in which 3D coordinate profiles areneeded.

As can be seen in FIG. 1, projection subassembly 14 projects radiationtoward the user, and a portion of this radiation may impinge on theuser's eyes. When coherent radiation is used for projection (which hasadvantages of high brightness and efficiency, particularly inconjunction with DOEs), it is important to ensure that the zero-ordercomponent does not exceed eye safety limits. The above-mentioned U.S.Patent Application Publication 2009/0185274, as well as U.S. patentapplication Ser. No. 12/840,312, filed Jul. 21, 2010, whose disclosureis incorporated herein by reference, describe optical designs that areuseful in reducing the zero-order intensity. It is still desirable,however, to monitor the performance of the projector so as to ensurethat the zero-order intensity remains within permissible limits.

Embodiment I

FIG. 2 is a schematic, sectional view of an optical pattern projector20, in accordance with an embodiment of the present invention. Thisprojector may be installed and used in place of subassembly 14 in device12 (FIG. 1). Projector 20 comprises a radiation source assembly 22,containing a laser diode and monitoring photodiode, which are describedin detail below with reference to FIGS. 3A and 3B. Assembly 22 ismounted on a base 24 and contained in a device package 26, along withthe other components of projector 20. These components include acollimating lens 28 and a DOE 30.

FIGS. 3A and 3B are schematic sectional and top views, respectively, ofradiation source assembly 22. A laser diode 40, which typically emitsinfrared radiation, is mounted on a submount 42, which is fixed to apackage stem 44 inside a “can” 46, such as a standard TO-56 can. Thelaser diode emits radiation through a window 48 in the upper side of thecan. An optical detector, in the form of a monitoring photodiode (MPD)50, is mounted in the can below the laser diode.

Referring back to FIG. 2, laser diode 40 emits an output beam 32 ofradiation, which is collimated by lens 28. DOE 30 diffracts thecollimated beam to generate a pattern comprising multiple diffractionorders, which is projected out through an exit window 34 of package 26.The projected beam includes a certain zero-order component (which theDOE may be designed to minimize). A portion of this zero-order componentis reflected back from the DOE into package 26. This portion isidentified as a reflected beam 36 in the figure.

To enable MPD 50 to sense this reflected zero-order component, DOE 30may be tilted slightly relative to the axis of beam 32. Typically, forthe purposes of the present embodiment, a tilt of 2-3° is sufficient(exaggerated for visual clarity in FIG. 2). This tilt has no significantimpact on the projected pattern, but it causes reflected beam 36 to beoffset from output beam 32, thereby striking MPD 50. The MPD outputs asignal, via a connector 38, in response to the intensity of thereflected beam. (Other pins on the same connector may be used to providethe driving current to the laser diode.) The intensity sensed by the MPDmay include components of one or more adjacent, higher diffractionorders. Alternatively, the MPD may be positioned so as to sensereflection of one or more of the higher diffraction orders instead ofthe zero order, and the higher-order intensity may provide an indicationof diffraction efficiency as in Embodiment II below.

A controller, such as processor 18 (FIG. 1), monitors the MPD signal. Ifthe signal level increases above a certain threshold level, thecontroller may conclude that the zero-order intensity of the projectorhas increased. The controller may then inhibit the operation ofprojector 20, typically by reducing or shutting off the driving currentto laser diode 40, in order to ensure that the intensity does not exceedthe permitted safety limit. Additionally or alternatively, thecontroller may issue an alarm to an operator of the projector or takeother appropriate action.

In the position of MPD 50 that is shown in FIGS. 3A and 3B, the MPD willreceive not only reflected beam 36, but also back-lobe emission fromlaser diode 40. In this configuration, the MPD may be used to monitorboth increases in the intensity of the zero order and decreases inoverall intensity that may result from to degradation of the laser diodeover time. If the MPD signal increases, the controller will inhibitprojector operation, as explained above. On the other hand, in the caseof a decrease in the MPD signal, the controller may increase the drivingcurrent to the laser diode in order to maintain the desired outputintensity of the projector.

Alternatively, if back-lobe monitoring of laser diode 40 is notrequired, MPD 50 may be shifted away from the laser diode, for examplefurther to the right in the view shown in FIG. 3A.

Embodiment II

FIG. 4 is a schematic, sectional view of an optical pattern projector60, in accordance with another embodiment of the present invention.Projector 60 and its components are similar in operation to projector20, except that in projector 60, the optical detector monitors thezero-order intensity indirectly, by sensing the intensity of one or morehigh diffraction orders transmitted by the DOE.

Projector 60 comprises a radiation source assembly 62, which typicallycontains a laser diode but may or may not contain a monitoringphotodiode. Assembly 62 is mounted on a base 64 and contained in adevice package 66, along with the other components of projector 20,including a collimating lens 68 and a DOE 70. The pattern generated byDOE 70 is projected through an exit window 72, which defines the angularrange of the projected pattern.

A monitoring photodiode (MPD) 74 senses one or more of the highdiffraction orders that are generated by DOE 70, at an angle that istypically outside the angular range of the projected pattern. Thesehigher orders are typically outside the field of view of the projector,and they are typically the first to decrease when the efficiency of theDOE begins to drop. In other words, if the diffraction efficiency of theDOE decreases, the intensity of the high-order diffracted radiationsensed by MPD 74 will also decrease. Such a decrease will typically beaccompanied by an increase of the zero-order intensity. Therefore, ifthe signal received by the controller (such as processor 18) from MPD 74drops below a permitted level, the controller will inhibit the drivingcurrent to the laser diode, as explained above.

FIG. 5 is a plot that schematically illustrates the performance of themonitoring function of MPD 74 in projector 60, in accordance with anembodiment of the present invention. The plot shows experimentalresults, in which the horizontal axis corresponds to the measuredzero-order optical power emitted from projector 60, and the decrease inthe current signal output from MPD 74, relative to a baseline value, isshown on the vertical axis. The plot demonstrates that the MPD signaldecrease is a reliable indicator of the increase in zero-orderintensity. When the MPD signal drops below a certain permitted range,the controller may conclude that the zero-order intensity has increaseddangerously and may then take the necessary steps to inhibit projectoroperation.

Although the above embodiments relate to certain specific projectorconfigurations and certain applications of such projectors, the use ofan integral optical detector for monitoring a certain diffraction ordermay likewise be used in other configurations and applications. It willthus be appreciated that the embodiments described above are cited byway of example, and that the present invention is not limited to whathas been particularly shown and described hereinabove. Rather, the scopeof the present invention includes both combinations and subcombinationsof the various features described hereinabove, as well as variations andmodifications thereof which would occur to persons skilled in the artupon reading the foregoing description and which are not disclosed inthe prior art.

The invention claimed is:
 1. Mapping apparatus, comprising: a projectionsubassembly, comprising: a device package; a radiation source, containedin the package and configured to emit a beam of coherent radiation; adiffractive optical element (DOE), mounted in the package so as toreceive and diffract the radiation from the radiation source into apredefined pattern comprising multiple diffraction orders; and anoptical detector, which is positioned in the package so as to receive aselected diffraction order of the DOE and to output a signal that isresponse to an intensity of the selected diffraction order; an imagingsubassembly, which is configured to capture an image of the pattern thatis projected onto an object; and processing circuitry, which isconfigured to process the image in order to produce a three-dimensional(3D) map of the object, and to process the signal in order to monitor aperformance of the DOE.
 2. The apparatus according to claim 1, whereinthe optical detector is configured to output a signal that is responsiveto the intensity, and comprising a controller, which is coupled toreceive and process the signal so as to monitor a performance of theapparatus.
 3. The apparatus according to claim 2, wherein the controlleris configured to inhibit an operation of the apparatus when the signalis outside a predefined range.
 4. The apparatus according to claim 1,wherein the radiation source comprises a laser diode.
 5. The apparatusaccording to claim 1, wherein the selected diffraction order is a zeroorder of the DOE.
 6. The apparatus according to claim 5, wherein theoptical detector is positioned so as to receive the zero order that isreflected back from the DOE.
 7. The apparatus according to claim 6,wherein the DOE is tilted relative to an axis of the beam emitted by theradiation source so as to direct the back-reflected zero order towardthe optical detector.
 8. The apparatus according to claim 1, wherein theselected diffraction order is a high order of the DOE.
 9. The apparatusaccording to claim 8, wherein the apparatus is configured to project thepattern over a predefined angular range, and wherein the opticaldetector is positioned to receive the radiation transmitted through theDOE at an angle that is outside the angular range.